Intelligent packet repetition in mobile satellite service (MSS) links to overcome channel blockages

ABSTRACT

Systems and methods for intelligent packet repetition in mobile satellite service links to overcome channel blockages. One example method includes transmitting and receiving packetized wireless communications between first and second communications devices via a bidirectional wireless link. The method includes receiving, by a first communications device from a second communications device, feedback information including an indication of a blockage in the communication channel, the indication including information indicating the presence and extent of the blockage, wherein the feedback does not include status indications for individual received packets. The method includes, responsive to receiving the indication of a blockage in the communication channel, determining a packet repeat value based on the feedback information, wherein the packet repeat value is greater than one. The method includes modifying a transmit signal of the bidirectional wireless link to repeat transmitted packets based on the packet repeat value and transmitting the downlink signal. The decision to turn on packet repetition, the number of repeats, may also be informed by the geographic location of the receiver.

RELATED APPLICATION

The present application is related to and claims benefit under 35 U.S.C.§ 119(e) from U.S. Provisional Patent Application Ser. No. 62/994,560,filed Mar. 25, 2020, titled “INTELLIGENT PACKET REPETITION IN MOBILESATELLITE SERVICE (MSS) LINKS TO OVERCOME CHANNEL BLOCKAGES,” the entirecontents of which being incorporated herein by reference.

FIELD

Embodiments described herein relate to satellite wireless communicationssystems and, more particularly, to providing intelligent packetrepetition in mobile satellite service (MSS) links to overcome channelblockages.

SUMMARY

Satellite communications systems and methods are widely used forcommunications with user equipment (UE). Satellite communicationssystems and methods generally employ at least one space-based component,such as one or more satellites, which are configured to wirelesslycommunicate with UEs on the Earth.

The overall design and operation of cellular satellite systems are wellknown to those having skill in the art and need not be described furtherherein. Moreover, as used herein, the term “UE” includes cellular orsatellite radiotelephones with or without a multi-line display; PersonalCommunications System (PCS) terminals (e.g., user terminals) that maycombine a radiotelephone with data processing, data communicationscapabilities; smart telephones that can include a radio frequencytransceiver and/or a global positioning system (GPS) receiver; and/orconventional portable computers or other electronic devices, whichdevices include a radio frequency transceiver. As used herein, the term“transceiver” may refer to a combined transmitter-receiver component ormay refer to devices that include separate transmitter and receivercomponents. A UE also includes any other radiating user device,equipment and/or source that may have time-varying or fixed geographiccoordinates and/or may be portable, transportable, installed in avehicle (aeronautical, maritime, or land-based) and/or situated and/orconfigured to operate locally and/or in a distributed fashion over oneor more terrestrial locations. Furthermore, as used herein, the term“space-based component” or “space-based system” includes one or moresatellites at any orbit (geostationary, substantially geostationary,medium earth orbit, low earth orbit, etc.) and/or one or more otherobjects and/or platforms (e.g., airplanes, balloons, unmanned vehicles,space crafts, missiles, etc.) that has/have a trajectory above the earthat any altitude.

Mobile satellite service (MSS) operates with relatively low link marginscompared to terrestrial wireless systems. This is because of the muchgreater propagation ranges involved in MSS relative to terrestrialwireless systems. A typical radio frequency propagation scenario for aterrestrial wireless system is illustrated in FIG. 1 . In FIG. 1 , a UE102 is in wireless communication with a transmission tower 104 via oneor more non-line-of-sight (NLOS) links 106. In terrestrial wirelesssystems, it is customary to operate with an approximately 20-30 dBmargin over a line-of-sight (LOS) link. However, as illustrated in FIG.1 , terrestrial links are normally of non-line-of-sight (NLOS) type.Radio propagation over NLOS links (e.g., the NLOS links 106) occursmostly by reflections from environmental clutter, for example, buildings108, trees (not shown), and the like. Terrestrial wireless links aredesigned so that, despite the direct path being blocked, enough signalpower still reaches the receiver of the UE 102 to close the link from ademodulation perspective. Therefore, useful information can be sent oversuch links. Link closure occurs despite the presence of substantial,excess attenuation and multipath fading relative to a LOS link.

In current systems, useful MSS propagation occurs mostly by LOS links,although some multipath reflection and diffraction may also be present,as illustrated in FIG. 2 . FIG. 2 shows a satellite 202 sending a signalto a vehicle mounted mobile satellite terminal 204 in an urban area 206.Although it is desirable to operate MSS in LOS conditions, this is notalways possible when the user equipment is mobile, for example, as shownin FIG. 2 . As illustrated in FIG. 2 , in urban areas, the signalreceived by the vehicle mounted mobile satellite terminal 204 may switchbetween LOS modes (e.g., receiving the signal via the LOS path 208) andNLOS modes (e.g., receiving the signal exclusively via the reflectedpaths 210) randomly as the line of sight path to the satellite 202 isintermittently blocked by buildings 212 and trees 214 as the vehiclemoves. The LOS channel also undergoes limited fading due to theenvironmental multipath, which may be present even when a direct path tothe transmitter is also present. This fading is characterized as Ricianand has much less depth than the Rayleigh fading present in NLOSchannels.

MSS propagation literature (e.g., Fernando Pérez Fontán, et al.,“Statistical Modeling of the LMS Channel”, IEEE TRANSACTIONS ONVEHICULAR TECHNOLOGY, VOL. 50, NO. 6, NOVEMBER 2001 p. 1549) hasidentified three major states (i.e., State 1, State 2, and State 3) forthe received signal, as illustrated in charts 302 and 304 of FIG. 3 .Chart 302 illustrates a received signal amplitude relative to LOS (indB) as a function of the traveled distance of the signal (in m). Chart304 illustrates a probability density function for a received signal asa function of the received signal amplitude relative to LOS (in dB). InState 1, the propagation mode is LOS. The signal has a mean valuerelative to a predetermined mean threshold value 306 that is sufficientto close the link with adequate margin (typically less than 4-5 dB) toaccommodate the Rician fading. If the UE is of handheld type, up to 10dB of link margin may be allowed for body absorption and lower antennadirectivity of the UE. In State 2, the direct path to the satellite maybe shadowed by tree foliage and subject to knife edge diffraction but noopaque blockage, such as by a building, is present; this is referred toas “shadowing” and results in an incremental pathloss over a clear LOSlink of approximately 4 dB. In State 3, the direct path is blocked,leading to typically greater than 15 dB additional pathloss, dependingon the nature of the building material.

To counter greater mean path loss and Rayleigh fading, terrestrialwireless links are operated with a link margin of 20-30 dB. This is aluxury that MSS links cannot afford owing to the large propagationdistance, the limited aggregate effective isotropic radiated power(EIRP) available on the satellite and the limited user equipment (UE)power. Hence, existing systems, especially for latency sensitiveapplications like voice, often resign themselves to acceptingintermittent blockage (e.g., increased pathloss caused by buildings,trees, and other environmental clutter) as a ‘fact of life.’ However,for data communications systems that can tolerate some increase intransport latency (e.g., over the 600 ms inherent round-trip delay of aGEO satellite link) time-interleaving has been used to mitigateintermittent channel blockage. For example, Inmarsat-C uses aninterleaving depth of 8 s.

Terrestrial wireless systems such as LTE, incorporate a feature known as“Hybrid Automatic Repeat reQuest,” or HARQ. HARQ requires aback-and-forth transaction between the transmitter and the receiver forevery repeat. In GEO MSS, with an approximately 600 ms round trip delay,implementing HARQ would impose a prohibitive latency and capacity cost.Note that, in terrestrial LTE, the round-trip delay (propagation delayplus HARQ processing time) is only few milliseconds. Therefore, HARQ andother terrestrial system solutions are not able to solve the problems ofchannel blockages in mobile satellite systems. Sending multiple packetrepetitions without an associated ARQ (blind repetition) is also used inLTE, but not as part of a dynamic, adaptive scheme. It is used tostatically optimize the link margin for a given UE, especially those indisadvantaged locations. These, blind repetitions, once configured, arestatic and not adaptive.

To address, among other things, these problems, systems and methods areprovided herein for intelligent packet repetition in mobile satelliteservice (MSS) links to overcome channel blockages. Embodiments describedherein provide, among other things, systems and methods for modifyingtransmit signals to adaptively repeat transmitted packets based onfeedback information and combine repeated packets at a receiver. Usingsuch embodiments results in, among other things, an increase insuccessful demodulation and decoding of the received packets.

One example embodiment discloses a wireless communications system. Thesystem includes a first communications device including a transceiverand an electronic processor. The electronic processor is configured totransmit and receive packetized wireless communications with a secondcommunications device via a bidirectional wireless link. The electronicprocessor is configured to receive, from the second communicationsdevice, feedback information including an indication of a blockage inthe communication channel, the indication including informationindicating the presence and extent of the blockage, wherein the feedbackdoes not include status indications for individual received packets. Theelectronic processor is configured to, responsive to receiving theindication of a blockage in the communication channel, determine apacket repeat value based on the feedback information, wherein thepacket repeat value is greater than one. The electronic processor isconfigured to modify a downlink signal of the bidirectional wirelesslink to repeat transmitted packets based on the packet repeat value. Theelectronic processor is configured to control the transceiver totransmit the downlink signal.

Another example embodiment discloses a method for intelligent packetrepetition. The method includes transmitting and receiving packetizedwireless communications between a first communications device and asecond communications device via a bidirectional wireless link. Themethod includes receiving, by the first communications device from thesecond communications device, feedback information including anindication of a blockage in the communication channel, the indicationincluding information indicating the presence and extent of theblockage, wherein the feedback does not include status indications forindividual received packets. The method includes, responsive toreceiving the indication of a blockage in the communication channel,determining a packet repeat value based on the feedback information,wherein the packet repeat value is greater than one. The method includesmodifying a downlink signal of the bidirectional wireless link to repeattransmitted packets based on the packet repeat value. The methodincludes transmitting the downlink signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a diagram of an RF signal propagation scenario for aterrestrial wireless network.

FIG. 2 is a diagram of an RF signal propagation scenario for an MSSwireless network.

FIG. 3 is a diagram of some example received signal states for an MSSwireless network.

FIG. 4 is a flow chart illustrating a method of packetized wirelesscommunications between two nodes according to some embodiments.

FIG. 5 is a diagram of a wireless communications system according tosome embodiments.

FIG. 6 is a chart illustrating aspects of the operation of the system ofFIG. 5 according to some embodiments.

FIG. 7 is a diagram illustrating a link adaptation method according tosome embodiments.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

Before any exemplary embodiments of the invention are explained indetail, it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement ofcomponents set forth in the following description or illustrated in thefollowing drawings. The invention is capable of other embodiments and ofbeing practiced or carried out in various ways.

It should also be noted that a plurality of hardware and software-baseddevices, as well as a plurality of different structural components maybe used to implement the invention. In addition, it should be understoodthat embodiments of the invention may include hardware, software, andelectronic components or modules that, for purposes of discussion, maybe illustrated and described as if the majority of the components wereimplemented solely in hardware. However, one of ordinary skill in theart, and based on a reading of this detailed description, wouldrecognize that, in at least one embodiment, the electronics basedaspects of the invention may be implemented in software (e.g., stored onnon-transitory computer-readable medium) executable by one or moreprocessors. As such, it should be noted that a plurality of hardware andsoftware-based devices, as well as a plurality of different structuralcomponents may be utilized to implement the invention. For example,“control units” and “controllers” described in the specification caninclude one or more processors, one or more memory modules includingnon-transitory computer-readable medium, one or more input/outputinterfaces, and various connections (e.g., a system bus) connecting thecomponents.

For ease of description, each of the example systems or devicespresented herein is illustrated with a single exemplar of each of itscomponent parts. Some examples may not describe or illustrate allcomponents of the systems. Other example embodiments may include more orfewer of each of the illustrated components, may combine somecomponents, or may include additional or alternative components.

As noted, methods used to mitigate channel blockage in terrestrialwireless systems may be ineffective for use with MSS wireless networks.Accordingly, embodiments provided herein provide systems that,responsive to the detection of channel blockage use adaptive packetrepetition at the transmitter and combining of the repeated packets atthe receiver to increase the probability of successfuldemodulation/decoding of the packet. As set forth herein, packets arerepeated only when required and the number of repetitions is dependenton the pathloss created by the blockage.

FIG. 4 is a flowchart illustrating a method 400 for intelligent packetrepetition. In some embodiments, the method 400 may be performed withrespect to a bidirectional wireless link between two nodes (e.g., asillustrated in FIG. 5 ). FIG. 5 schematically illustrates a wirelesscommunications system 500. The wireless communications system 500includes two nodes, Node A and Node B. Node A and Node B arecommunications device, which communicate via a bidirectional wirelesslink 502. In some embodiments, Node A and Node B are part of a largerwireless network (e.g., an MSS network). In one example MSS-relatedembodiment, Node A is a satellite or a hub (also referred to as agateway) of a satellite network and Node B is a UE of the satellitenetwork.

Node A includes a baseband processor 504, a transceiver 506, and anantenna 508. The baseband processor 504 includes digital signalprocessors (DSPs) and other hardware or software suitable to perform themethods described herein. In some embodiments, the baseband processor504 controls the transceiver 506 to transmit and receive voice, video,and other data to and from Node B. The baseband processor 504 encodesand decodes digital data sent and received by the transceiver 506. Thetransceiver 506 transmits and receives radio signals to and from, forexample, Node B using the antenna 508. The baseband processor 504 andthe transceiver 506 may include various digital and analog components(e.g., memory and input-output (I/O) ports), which for brevity are notdescribed herein and which may be implemented in hardware, software, ora combination of both. Similarly, Node A includes other hardware andsoftware components not described herein. Some embodiments includeseparate transmitting and receiving components, for example, atransmitter and a receiver, instead of a combined transceiver 506. NodeB includes a baseband processor 510, a transceiver 512, and an antenna514. The components of Node B are similar to their correspondingcomponents in Node A and are configured to operate in a similar fashionaccording to embodiments described herein.

Embodiments described herein, including the method 400, may beimplemented by the baseband processors 504, 510 or by generalmicroprocessors, also referred to as central processing units (CPUs)(not shown), coupled to the baseband processors 504, 510 and othercomponents of Node A and Node B. The system 500 described is but oneexample. Other implementations (including hardware, software, orcombinations thereof) are possible. The inventive concepts set forthherein apply to other implementation approaches.

Relative to the MSS-related embodiment, the methods described herein maybe applied to both the forward link (FL) (also referred to as thedownlink (DL)) and to the return link (RL) (also referred to as theuplink (UL)). As used herein, the term “link” refers to the service link(e.g., the satellite-to-UE link). In more general terms, for both theforward and return links of the service link, the term “transmitter” mayrefer to satellite for FL or UE for RL, and the term “receiver” mayrefer to UE for FL or satellite for RL.

Returning to FIG. 4 , one embodiment of the method 400 is now described.By way of example, the method 400 is described in terms of an MSS usecase, where Node A is a satellite and Node B is a UE. In particular, themethod 400 is described as being performed by the baseband processor 510of Node B. However, it should be understood that in some embodiments,portions of the method 400 may be performed by other devices, includingfor example, Node A. For ease of description, the method 400 isdescribed in terms of an MSS including only two nodes. However, themethod 400 may be applied to an MSS including multiple satellites andtens, hundreds, or even thousands of UEs. In addition, as noted, themethod 400 is applicable to other use cases.

At block 402, the baseband processor 510 estimates the mean value of thereceived signal (referred to herein as the Mean_Value). Note that, inthe MSS case, “link” refers to the service link (i.e., thesatellite-to-UE link). In some embodiments, the baseband processor 510determines the Mean_Value by receiving and processing a sounding signal(also referred to as pilot signal), at the transceiver 512.

A Mean_Value may be determined in both the forward and return links byreceiving and processing a sounding signal. For example, in the forwardlink, the sounding signal is generated and transmitted by a satellitebase station subsystem (S-BSS), relayed by the satellite (e.g., Node Aof FIG. 5 ), and received and processed by the UE (e.g., Node B of FIG.5 ). In another example, for the return link, the sounding signal isgenerated and transmitted by the UE (e.g., Node B of FIG. 5 ), relayedby the satellite (e.g., Node A of FIG. 5 ) and received/processed by theS-BSS. As used herein, relaying a signal means receiving the signal,amplifying and frequency shifting the signal, and transmitting thesignal at the shifted frequency. In some embodiments, it is desirablethat the sounding signal be of spread spectrum type, such as apseudo-noise (PN) signal, so that the signal can be received, and thepathloss measured reliably, even when the power spectral density (PSD)of the received PN signal, S, is well below that of the ambient noiseand interference (N+I). The spread spectrum gain of the PN signalenables reliable signal reception with negative S/(N+I) PSD ratios. Thisprovides a large dynamic range for pathloss measurement. The processingof the spread spectrum signal (i.e., the operations of signalacquisition and dispreading) may be performed according to knowntechniques.

At block 404, the baseband processor 512 determines whether theMean_Value (determined at block 402) is less than a first thresholdvalue (referred to herein as the Mean_Threshold_Value). For example, thebaseband processor 510 compares numerical values for the Mean_Value andthe Mean_Threshold_Value. In some embodiments, the Mean_Threshold_Valueis set to a fixed, empirically determined value. In other embodiments,the Mean_Threshold_Value may be determined automatically by, forexample, using machine learning methods. For example, Node B or anothercomponent of the wireless communications system 500 (e.g., a computerserver) may use various machine learning methods to analyze historicalMean_Value data points stored in a memory and/or a database to makedeterminations regarding the Mean_Threshold_Value.

Machine learning generally refers to the ability of a computer programto learn without being explicitly programmed. In some embodiments, acomputer program (sometimes referred to as a learning engine) isconfigured to construct a model (for example, one or more algorithms)based on example inputs. Supervised learning involves presenting acomputer program with example inputs and their desired (actual) outputs.The computer program is configured to learn a general rule (a model)that maps the inputs to the outputs in the training data. Machinelearning may be performed using various types of methods and mechanisms.Example methods and mechanisms include decision tree learning,association rule learning, artificial neural networks, inductive logicprogramming, support vector machines, clustering, Bayesian networks,reinforcement learning, representation learning, similarity and metriclearning, sparse dictionary learning, and genetic algorithms. Using someor all of these approaches, a computer program may ingest, parse, andunderstand data and progressively refine models for data analytics,including image analytics. Once trained, the computer system may bereferred to as, among other things, an intelligent system, an artificialintelligence (AI) system, a cognitive system, or an intelligent agent.

In some embodiments, an intelligent agent analyzes the accumulatedhistory of the Mean_Value over some observation time (T_obs) for which atypical value might be 15 minutes, and which is informed by the loadingof the spotbeam in which the UE is located over a similar observationperiod. In some embodiments, the intelligent agent computes aprobability distribution function (PDF) of Mean_Value over T_obs, toproduce a chart, such as the chart 304 shown in the inset in FIG. 3 .This PDF may be used to determine the Mean_Threshold_Value. In someembodiments, the Mean_Threshold_Value may be chosen by using criteriasuch as: at any time, the increased load on the network due to packetrepetition must not cause the network load to reach more than 70% of theavailable capacity. Machine Learning may be used to inform the selectionof Mean_Threshold_Value.

When Mean_Value is not less than the Mean_Threshold_Value (at block404), the baseband processor 510 (at block 406) determines that nopacket repetitions are necessary and sets the value of a packet repeatvalue (N_Repeat) to 1 (representing a single transmission, withoutrepetition). The value of N_Repeat is used by the baseband processor 510to control how many times a packet is re-transmitted. The value ofN_Repeat is communicated by Node B 510 (the receiver in this example) toNode A 504 (the transmitter in this example).

When Mean_Value is less than the Mean_Threshold_Value (at block 404),the baseband processor 510 (at block 408) determines a Deficit_Value forthe link. The Deficit_Value is the difference between Mean_Value andMean_Threshold_Value:Deficit_Value=Mean_Threshold_Value−Mean_Value.  (1)

Note that Deficit_Value is always a positive number.

At block 410, the baseband processor 504 determines whether theDeficit_Value (determined at block 408) is less than a second thresholdvalue (referred to herein as the Deficit_Threshold_Value). For example,the baseband processor 504 compares numerical values for theDeficit_Value and the Deficit_Threshold_Value. It is possible for thelink margin deficit (represented by Deficit_Value) to exceed the valuebeyond which mitigation is deemed either technically infeasible orundesirable based on the capacity expenditure required. An exampleDeficit_Threshold_Value may be 30 dB. In some embodiments, theDeficit_Threshold_Value is set to a fixed, empirically determined value.In other embodiments, the Deficit_Threshold_Value is set automatically,for example by using machine learning methods to analyze historical data(including link margin deficit values, related N_Repeat values, and dataindicating packet demodulation and decoding success or error rates).

When Deficit_Value is not less than the Deficit_Threshold_Value (atblock 410), the baseband processor 510 returns to block 402 and beginsdetermining and processing another Mean_Value for the link's pathloss.

When Deficit_Value is less than the Deficit_Threshold_Value (at block410), the baseband processor 504 (at block 412) determines an N_Repeatvalue, which indicates a specific number of repetitions to be applied topacket transmissions. In some embodiments, N_Repeat is determined as afunction F of the Deficit_Value: N_Repeat=F(Deficit_Value).

As noted, the Deficit_Threshold_Value is an upper limit beyond whichpacket repetitions are unlikely to yield practical benefits or thecapacity tax may be too high. In some embodiments, F(Deficit_Value) isdetermined based on the effectiveness of packet repetition andrecombination. Methods of combining of repeated packets are known in theprior art. The available options include fully coherent combining andpartially coherent/partially incoherent combining. The method chosen hasimplications for the receiver processor, with fully coherent combiningbeing more challenging to implement but yielding more link margin.

As noted, in some embodiments, the tasks required to sense the presenceand depth of blockage, and determine N_Repeat as described in FIG. 4 ,may be differently apportioned between the receiver (Node B) and thetransmitter (Node A) than described above. Specifically, the role of thereceiver (Node B) may be limited to sensing a channel quality indicatorparameter (CQI), which is indicative of the received SNIR—hence thedepth of blockage—and communicating the CQI to the transmitter (Node A).Node A may construct a profile of the received SNIR based on thereported CQI and determine all parameters necessary to execute the flowdiagram of FIG. 4 , including Mean_Value of pathloss andMean_Threshold_Value. This approach may be preferred in embodimentsseeking to maintain affinity to existing standards, as CQI measurementby a receiver and feedback to the transmitter is supported in cellularstandards, such as LTE and 5GNR.

Regardless of the packet combining method used, a graph of ReceivedSignal-to-Noise Ratio (SNR) versus Packet Error Rate for differentnumbers of packet repetitions can be constructed to determine thefunction F. FIG. 6 illustrates an example SNR v. PER graph 600. Asillustrated in FIG. 6 , the functional relationship betweenDeficit_Value and N_Repeat can be established. FIG. 6 shows the examplefor N_Repeat=100. It should be noted that the graph 600 is an exampleprovided solely to explain the concept and does not provide dataspecific to any particular system. Accordingly, the ‘Received SNR’ axishas no scale.

The functional roles described above with respect to blocks 401-412 ofFIG. 4 may be distributed between the transmitter and the receiver invarious combinations. For example, in one embodiment, the receiverperforms the Mean_Value estimation, based on signals received on the FLand communicates it back to the transmitter using the RL. Thetransmitter performs all other functions, including selecting N_Repeat.In another example embodiment, the receiver performs all functions,including selecting the value of N_Repeat. The N_Repeat value iscommunicated by the receiver to the transmitter.

Regardless of how the functions are distributed between the transmitterand the receiver, from the time of onset of a blockage, a latency of oneround trip delay plus processing time (typically less than 10 ms) isunavoidable before the link margin enhancement will take effect. For aGEO satellite link, this will amount to approximately 600 ms. GEO MSSchannel characterization campaigns have shown that the blockage durationin urban environments is greater than 5 s for more than 20% of the time(see, e.g., Erich Lutz, et al., “The Land Mobile Satellite CommunicationChannel-Recording, Statistics, and Channel Model,” IEEE TRANSACTIONS ONVEHICULAR TECHNOLOGY, VOL. 40. NO. 2, MAY 1991 p. 315), where ‘blockage’is defined as a 5-dB loss in the received SNR. This means that thereaction latency would be limited to 12% of the blockage duration.Therefore, the methods of the present invention have the potential tomake a material improvement to link closure probability in suchenvironments without levying an excessive capacity tax.

Implementation of the proposed adaptive packet repetition method maydepend on the various embodiments of the system, which would havedifferent impact on the system performance, operation procedures andcontrol signaling between the receiver and the transmitter.

In one example embodiment, the receiver would make the decision as tohow many repetitions were needed based on the measurement of theMean_Value as described herein. The repetition decision is conveyed tothe transmitter through return control channel to take the aboverepetition action. On the transmitter side, where the transmissionrepetition takes place, the transmitter needs to let the receiver knowthrough forward control channel where in the time frame, that is,exactly when the repetition begins, so that the receiver can demodulatethe received stream correctly.

In another embodiment but still pertaining to the case where thereceiver is selecting the degree of repetition and informing thetransmitter, instead of specifying an N_Repeat value, the receiver mayset an Update_Timer that is equal to the transmission repetition time(TRT) corresponding to the duration over which repetition is made. TheTRT is given by the product of N_Repeat and the duration of the repeatedpacket of minimum size (the atomic transmitted unit), referred to asMinimum Transmission Block. After the Update_Timer expires, the receiverwill update the N_Repeat value following the procedures described withrespect to FIG. 4 . Specifically, this means updating the transmitterwith information about the next step, i.e., whether or not continue toperform repetition with an updated TRT (corresponding to an updatedN_Repeat). If the receiver decides that there is a need to continue toperform repetition at the end of the timer, then the Update_Timer isreset to the new TRT, corresponding to the updated N_Repeat. If receiverdecides that no more repetition is needed, as per the flow diagram ofFIG. 4 , the receiver updates the transmitter with information thatN_Repeat=1, or the corresponding value of TRT, which are the defaultvalues for normal channel condition. FIG. 7 illustrates a graph 700,which includes a link adaption trace 702 according to such anembodiment, assuming the mean received-signal time-variation levelprofile shown in the top trace. As illustrated in FIG. 7 , the abovedescribed embodiments would make transmission repetition adaptive to thechannel condition without the need to make a repetition decision afterthe receipt of every Minimum Transmission Block, unlike HARQ. This is avery efficient way to achieve near optimal performance in randomlyblocked channels, which is absent in the prior art.

As discussed herein, due to the reaction latency of 600 ms, for somesituations where the channel conditions may switch rapidly between State1, State 2 and State 3, the embodiment illustrated in FIG. 7 may notwork well. Other possible embodiments may be more robust for these typesof situations. For example, in another embodiment, once a receiverdetermines that a such channel condition is present by examining thereceived signal level or by the geographic location of the receiver,which may be known to involve a high probability of blockage, thereceiver may decide to instruct the transmitter to keep doing a blindtransmission repetition for a certain period of time regardless of thereceived signal level to ride out rapidly varying channel conditions.The receiver may set the Update_Timer to the period of time duration atthe beginning, and by the end of the timer, the receiver wouldre-evaluate the channel condition, and decide the next step accordingly.Alternatively, the start and end of blind repetitions could bedetermined by receiver location, or some combination of the abovefactors. For example, it may be known a priori that certain stretches ofa road, or areas of an urban area, are so heavily blocked that it wouldbe best to turn on a certain level of repetition (say 8 repeats of eachpacket) everywhere in the above locations.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

Moreover in this specification, relational terms for example, first andsecond, top and bottom, and the like may be used solely to distinguishone entity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has,”“having,” “includes,” “including,” “contains,” “containing,” or anyother variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises, has, includes, contains a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” or“contains . . . a,” does not, without more constraints, preclude theexistence of additional identical elements in the process, method,article, or apparatus that comprises, has, includes, contains theelement. The terms “a” and “an” are defined as one or more unlessexplicitly stated otherwise herein. The terms “substantially,”“essentially,” “approximately,” “about,” or any other version thereof,are defined as being close to as understood by one of ordinary skill inthe art, and in one non-limiting embodiment the term is defined to bewithin 10%, in another embodiment within 5%, in another embodimentwithin 1% and in another embodiment within 0.5%. The term “coupled” asused herein is defined as connected, although not necessarily directlyand not necessarily mechanically. A device or structure that is“configured” in a certain way is configured in at least that way but mayalso be configured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore general purpose or specialized processors (or “processing devices”)such as microprocessors, digital signal processors, customizedprocessors and field programmable gate arrays (FPGAs) and unique storedprogram instructions (including both software and firmware) that controlthe one or more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of thesystems, methods and/or devices described herein. Alternatively, some orall functions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the foregoing approaches could be used.

Various features and advantages of some embodiments are set forth in thefollowing claims.

What is claimed is:
 1. A wireless communications system comprising: abidirectional wireless link between two transceivers containingelectronic processors, configured to transmit and receive packetizedwireless communications, wherein a receiver of one transceiver providesfeedback information to a transmitter of the other transceiver, based onwhich information: a determination is made using the transceivers'electronic processors determine: that the bidirectional wireless link issubject to blockage, an extent of the blockage, and a packet repeatvalue indicative of a number of packet repetitions necessary to enablethe receiver to receive transmitted packets with adequate reliability bypacket combining, and subsequent to the said determination, thetransmitter sends the transmitted packets to the receiver based on thepacket repeat value.
 2. The wireless communication system of claim 1,wherein the determination of the packet repeat value is made at thereceiver.
 3. The wireless communication system of claim 2, wherein thedetermination of the packet repeat value is made at the transmitter. 4.The system of claim 1, wherein the electronic processors are configuredto: determine the packet repeat value by: estimating a mean pathlossvalue for a transmitted signal of the bidirectional wireless link;determining whether the mean pathloss value is less than a firstthreshold; responsive to determining that the mean pathloss value isless than the first threshold, determining a deficit value for thetransmitted signal; determining whether the deficit value is less than asecond threshold; responsive to determining that the deficit value isless than the second threshold, determining the packet repeat valuebased on a functional relationship between the deficit value and anumber of packet repetitions.
 5. The system of claim 4, wherein theelectronic processors are configured to determine the deficit valuecalculating a difference between the first threshold value and the meanpathloss value.
 6. The system of claim 4, wherein the functionalrelationship is based on an estimate of the packet error rate for thetransmitted signal and a received signal to noise ratio for thetransmitted signal at a receiver of the second communications device. 7.The system of claim 4, wherein the first threshold is set to a staticvalue.
 8. The system of claim 4, wherein the first threshold isdetermined dynamically using a machine learning model trained usinghistorical mean pathloss values for the transmitted signal.
 9. Thesystem of claim 1, wherein the electronic processors are configured to:set an update timer based on a transmission repetition time; andresponsive to the update timer expiring, determine an updated packetrepeat value.
 10. The system of claim 8, wherein the transmissionrepetition time is based on the packet repeat value and a minimumtransmission block.
 11. The system of claim 1, wherein the wirelesscommunications system is part of a mobile satellite system.
 12. Thesystem of claim 1, wherein the decision to repeat packets and the packetrepeat value are informed by the geographic location of the receivingtransceiver.
 13. A method for intelligent packet repetition, the methodcomprising: transmitting and receiving packetized wirelesscommunications between a first communications device and a secondcommunications device via a bidirectional wireless link; receiving, bythe first communications device from the second communications device,feedback information including an indication of a blockage in thecommunication channel, the indication including information indicating apresence and an extent of the blockage, wherein the feedback does notinclude status indications for individual received packets; responsiveto receiving the indication of a blockage in the communication channel,determining a packet repeat value based on the feedback information,wherein the packet repeat value is greater than one; modifying adownlink signal of the bidirectional wireless link to repeat transmittedpackets based on the packet repeat value; and transmitting the downlinksignal.
 14. The method of claim 13, wherein determining the packetrepeat value includes: estimating a mean pathloss value for the downlinksignal; determining whether the mean pathloss value is less than a firstthreshold; responsive to determining that the mean pathloss value isless than the first threshold, determining a deficit value for thedownlink signal; determining whether the deficit value is less than asecond threshold; responsive to determining that the deficit value isless than the second threshold, determining the packet repeat valuebased on a functional relationship between the deficit value and anumber of packet repetitions.
 15. The method of claim 14, whereindetermining the deficit value includes calculating a difference betweenthe first threshold value and the mean pathloss value.
 16. The method ofclaim 14, wherein the functional relationship is based on an estimate ofthe packet error rate for the downlink signal and a received signal tonoise ratio for the downlink signal at a receiver of the secondcommunications device.
 17. The method of claim 14, wherein the firstthreshold is set to a static value.
 18. The method of claim 14, furthercomprising: determining the first threshold dynamically using a machinelearning model trained using historical mean pathloss values for thedownlink signal.
 19. The method of claim 12, wherein the determinationof the packet repeat value is performed by the second communicationsdevice.
 20. The method of claim 19, further comprising: setting anupdate timer based on a transmission repetition time; and responsive tothe update timer expiring, determining an updated packet repeat value.21. The method of claim 20, wherein the transmission repetition time isbased on the packet repeat value and a minimum transmission block. 22.The method of claim 12, where the first communications device and thesecond communications device belong to a mobile satellite system.